From your description, as long as the battery will maintain above 9.5 volts during cranking and the connections are good at the battery and the starter. Most likely the starter has failed. Try tapping on the starter while some one cranks the engine over, if the starter engages the starter is going bad and needs to be replaced. If the oil is very low, verify you can turn the engine over by hand. Engines that have been run with no oil may lock up.

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